LOS ANGELES — Jean and Scott Adam sailed their 58-foot yacht for months at a time, patching together an enviable life of exotic sights and bluewater adventure, imbued with devout faith.

For every busted alternator or arduous dive to wipe muck from the propeller, there was a breathless report to friends from another remote locale — Kota Kinabalu, Micronesian archipelagos.

But beneath that veneer of whim and wonder, a hard and dark reality loomed. The couple were in their seventh year of an off-and-on, round-the-world trip, and at some point, that would mean crossing through the Indian Ocean and the Gulf of Aden — a shipping route known as “Pirates Alley.”

On Tuesday, in a chaotic storm of grenades, gunfire and hand-to-hand combat, the couple were killed aboard their beloved sloop, Quest, by Somali pirates, according to the U.S. military. He was 70; she was 66.

Friends from Seattle — Phyllis Macay, 59, and Bob Riggle, 67 — also were killed, as were four pirates. At least 13 pirates were taken into U.S. custody and are expected to face prosecution.

Accounts of the killings varied Tuesday and could take some time to sort out.

The Adams were headed toward the Red Sea then the Greek islands Friday when, according to U.S. military officials, pirates boarded Quest off the coast of Oman.

Almost immediately, U.S. Navy vessels began shadowing the yacht, negotiating for the Americans’ release as the vessels made their way southwest toward Somalia, said Lt. Col. Mike Lawhorn, a spokesman for U.S. Central Command, part of an international coalition of anti-piracy operations in the Indian Ocean.

There were signs of dissent among the pirates. Two of them abandoned the yacht Monday and came aboard the USS Sterett, a guided-missile destroyer.

Then Tuesday morning, the pirates fired an errant rocket-propelled grenade at the Sterett, according to the U.S. military. As some pirates came on deck with hands raised, as if trying to surrender, a team of 15 Navy SEALs boarded the yacht amid small-arms fire.

President Obama had authorized the use of force if the military determined the hostages’ lives were in imminent danger, the White House said.

“The intent always had been that this would be a negotiated process and not ever go into a point where we actually had gunfire,” said Vice Adm. Mark Fox, commander of U.S. naval forces in the region.

When U.S. special-operations forces boarded the yacht, they found two pirates dead. Military forces killed two others, one with a gun and one with a knife.

All four hostages had been shot. Some were alive and were given medical treatment, but all died, U.S. officials said. Their bodies were taken aboard the U.S. aircraft carrier USS Enterprise and were expected to be transported to the United States.

The pirates offered a different account. Liban Muse, a member of the group involved in the incident, told the Los Angeles Times in a telephone interview from the Somali coast that the U.S. military fired first.

“We had no intention of killing the hostages until the Americans began shooting at us,” Muse said. “Our preference is only to take ships and ransom money, not to kill. But governments are targeting and killing our people.”

Lawhorn, the Central Command spokesman, dismissed those claims.

Piracy has exploded in the Gulf of Aden in the past decade, impeding goods delivery in a vital shipping corridor and driving up costs. Over the past four years, a coalition of two dozen governments has pieced together a robust military response, with mixed results.

Many areas of the Gulf have indeed become safer. But pirates — driven largely by ransoms, but also by a sense of nationalism and protectionism — have responded by expanding their operations into once-safe pockets of the Indian Ocean.

Some also have responded with increased sophistication, improving communication and buying larger vessels that serve as “mother ships,” floating headquarters of sorts.

The pirates also have developed a more acute understanding of the region’s sailing patterns — including the fact that to avoid monsoons and other dangerous conditions, pleasure-boat “cruisers” such as the one owned by the Adams must navigate the area in the early months of the year.

Still, few hostage incidents end in death, prompting speculation that something went wrong either because the pirates turned on each other or the Americans attempted to escape or fight their way to freedom.

A U.S. military official said there was no indication the hostages had tried to overpower the pirates.

The Adams were well aware of the piracy threat. Scott Adam had considered shipping their boat atop a cargo vessel to avoid the dangers, a friend said.

And in January, the day before she flew to Thailand to rejoin her husband on their voyage, Jean Adam, a dentist, discussed piracy with an old friend over lunch a in the Venice section of Los Angeles.

“I said: ‘Aren’t you worried?’ ” said Marilyn Blacker, who worked as a dental hygienist in Jean Adam’s Santa Monica office for years. “She was very matter-of-fact. She said they were going with this rally, that they’ve done this before.”

Scott Adam grew up in Chicago and worked for 30 years in episodic television and films, then left it behind in 1996 after undergoing a “mystical experience where God was calling him to ministry,” said Richard Peace, a professor at Fuller Theological Seminary and a close friend of the Adams’.

In the late 1990s, he was introduced by a mutual friend to Jean Adam, then named Jean Savage. They were married soon after; both had children from a previous marriage.

Their missionary work eventually became intertwined with their love of sailing, Peace said. They began traveling the world with armloads of Bibles.